Phthalocyanine compounds are useful materials as a paint, a printing ink, a catalyst, and an electronic material, and recently phthalocyanine compounds have been widely investigated as a material for an electrophotographic photoreceptor, a material for a photo-recording material and a material for a photoelectric conversion element.
In the field of an electrophotographic photosensitive material, there has been recently demanded that the photosensitive wavelength region of organic photoconductive materials which are hitherto been proposed is extended to the wavelength (780 to 830 nm) of a near infrared semiconductor laser, so as to use them as an electrophotographic photosensitive material for a photoreceptor for digital recording such as laser printer, etc. From the view point, squarylium compounds (as described in JP-A-49-105536 and JP-A-58-21416), triphenylamine series trisazo compounds (as described in JP-A-61-151659), phthalocyanine compounds (as described in JP-A-48-34189 and JP-A-57-148745), etc., have been proposed as organic photoconductive materials for semiconductor laser. The term "JP-A" as used herein means an "unexamined published Japanese patent application".
When an organic photoconductive material is used as a photosensitive material for semiconductor laser, it is required that the light-sensitive wavelength region extends to a long wavelength region, and the electrophotographic photoreceptor formed has a high sensitivity and a good durability. However, the organic photoconductive materials described above do not sufficiently meet these requirements.
For overcoming the above faults of the foregoing organic photoconductive materials, the relationships between the crystal forms and the electrophotographic characteristics have been investigated and, in particular, many reports have been made with respect to phthalocyanine compounds.
It is known that phthalocyanine compounds generally show various crystal forms according to the differences of the production methods and the treatment methods and it is also known that the difference in the crystal forms gives a large influence on the photoelectric conversion characteristics of the phthalocyanine. In regard to the crystal forms of copper phthalocyanine compounds, the crystal forms of .alpha., .pi., .chi., .rho., .gamma., .delta., etc., are known in addition to the stable .beta. form and it is known that these crystal forms can be transformed to each other by a mechanical strain force, a sulfuric acid treatment, an organic solvent treatment, a heat treatment, etc., as described, e.g., in U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989. JP-A-50-38543 describes the relationship between the difference in the crystal form of copper phthalocyanine and the electrophotographic sensitivity. Furthermore, gallium phthalocyanine is described in JP-B-3-30853 and JP-B-3-30854 (the "JP-B" as used herein means an "examined published Japanese patent application") and also the electrophotographic characteristics of the crystal forms thereof are described in JP-A-1-221459.
However, when not only the foregoing crystal forms of gallium phthalocyanine but also conventionally proposed phthalocyanine compounds are used as photosensitive materials for electrophotographic photoreceptors, the light sensitivity and the durability are yet insufficient.
Accordingly, the development of novel phthalocyanine compounds suitable for photosensitive materials having improved light sensitivity and the durability while utilizing the features of the foregoing phthalocyanine compounds has been desired. The present invention has been made for solving the foregoing problems in the conventional techniques.